1. Field of the Invention
The invention concerns a device for keeping an inkjet print head for franking and/or addressing machines clean, in particular the surface with the nozzle exit openings therein.
2. Description of the Prior Art
It has proven valuable to utilize the advantages of inkjet printing in the field of machine franking and/or addressing. The printing ensues without contact by means of an inkjet print head (see for example DE 44 24 771 C1 and EP 0 696 509 B1). However, the inkjet printing technique has the disadvantage that, in addition to the free spraying of the nozzles, the surface with the nozzle exit openings—called a nozzle surface for short in the following—must be regularly cleaned in order to prevent a choking of the nozzles and to ensure a secure sealing by the sealing cap.
Ink mist and paper dust deposits increasingly occur during the printing operation, and ink deposits increasingly occur during priming. The quick-drying ink in connection with the paper dust leads to contaminations at the typical operating temperature of 40° C. of the inkjet print heads, which contaminations are difficult to remove. Repeated wiping is necessary for this purpose. During this time, the machine is not available for the normal operation. Such downtimes reduce the letter throughput.
A device for cleaning an inkjet print head in a franking and/or addressing machine is known (see EP 1 782 954 A1) in which the inkjet print head is arranged stationary but pivotable in a print window or guide plate for the print substrate. The inkjet print head is selectively pivotable into a printing position or into various cleaning areas as well into a sealing position by means of associated displacement means (see also FIG. 1 in the following).
A cleaning and sealing device 13 (CSD in the following) is likewise arranged behind the guide plate (not shown) but below the inkjet print head 110. The CSD 13 is moved towards the inkjet print head 110 and away from this again by means of associated displacement means. The CSD 13 has a receptacle 131 with multiple wiper lips 1311 situated one after another, a spray duct 1312 and a sealing cap 1313 that are arranged in the cited order behind the guide plate.
In the cleaning region adjacent to the sealing position, the inkjet print head 110 is pivoted out of the printing position so far that the nozzle surface 111 lies in the engagement region of the wiper ellipsoid 1311 that slide along on the nozzle surface 111 in the cleaning operation. In order to achieve a thorough cleaning, the nozzle surface 111 must be repeatedly wiped in spite of multiple wiper lips 1311. This involves long downtimes. In the sealing position, the nozzle surface 111 is arranged orthogonal to the wiper lips 1311.
A carrier 1317 with strippers 13171 that is arranged stationary in the engagement region of the wiper lips 1317, above said wiper lips 1317, is in turn provided to clean the wiper lips 1317. After the cleaning operation, the wiper lips 1317 are directed towards the strippers 13171. The wiper residues can fall into an ink sump located under the CSD 13.
Furthermore, a device to clean inkjet nozzles of an inkjet print head of a franking machine is known (see EP 1 504 905 B1) that has a means to abrade the nozzle surface. The means is an impeller that slides with its blades along the nozzle surface of the inkjet print head arranged stationary in a printing window after at least one mail piece has passed the inkjet print head.
Contacting the inkjet print head and rotation movement of the impeller are triggered by the mail piece. In this way the impeller can be pivoted between an abrading position in which it is arranged in the transport path of the mail pieces in the franking machine and a rest position in which it is drawn back from the transport path. The impeller is consequently always arranged more or less far into a region in front of the inkjet print head. The cleaning device moreover comprises a scraper [ductor] to clean the blades of the impeller.
The impeller is mounted on pivoting support arm which can move between the scraper position and the rest position. The movement of the pivot support arm is controlled dependent on the number of mail pieces counted by a position sensor. The position sensor is mounted in the transport path of the maul pieces and controls an electromagnet that is coupled with the pivot arm. The impeller has a torque motor.
However, the disadvantages outweigh the advantages of short paths and downtimes for the cleaning process. The transport region is thus contaminated by the rotating impeller in the cleaning process. Since the impeller is only centrally placed in the region of the nozzle series due to the pivot movement onto the nozzle surface, the edge regions are either not contacted at all or, respectively, are contacted only with slight force at correspondingly larger circumference. This results in an incomplete cleaning of the nozzle surface. The technical expenditure is considerable. The expenditure for the cleaning doubles given use of two inkjet print heads for the purpose of printing longer columns.